New microfabrication techniques are being developed in recent years for the increasingly higher integration and higher performance of semiconductor integrated circuits (hereinafter referred to as “LSI”). One such technique is Chemical Mechanical Polishing (CMP), the technique often used for flattening of interlayer insulating films, formation of metal plugs and formation of embedded wirings in LSI production steps, particularly in multilayer wiring forming steps (see Patent literature 1 below, for example).
Recently, it has been attempted to utilize copper-based metals as wiring materials to increase performance of LSIs. Copper-based metals, however, are poorly suitable for microfabrication by dry etching which is often used for forming conventional aluminum alloy wiring. The “damascene method” has therefore been largely employed for microfabrication of copper-based metals, in which method a thin-film of a copper-based metal is accumulated on an insulating film having pre-formed furrows (concavities) and elevated sections (convexities) to embed the copper-based metal in the furrows, and then the thin-film accumulated on the elevated sections (the thin-film on sections other than the furrows) is removed by CMP to form embedded wiring (see Patent literature 2 below, for example).
The common method of CMP for polishing of wiring section metals such as copper-based metals involves attaching a polishing cloth (polishing pad) onto a circular platen, dipping the polishing cloth surface into a polishing solution for metal films, pressing the metal film-formed surface of a substrate against the polishing cloth surface, rotating the platen with a prescribed pressure (hereunder referred to as “polishing load” or “polishing pressure”) being applied to the metal film from the back side of the substrate, and removing the metal film on the elevated sections by mechanical friction between the polishing solution and the metal film on the elevated sections.
A polishing solution for metal films used for CMP usually comprises an oxidizing agent, a solid abrasive (hereunder referred to simply as “abrasive”) and water, with a metal oxide solubilizer, metal corrosion preventing agent and the like if necessary. The basic mechanism of CMP employing a polishing solution for metal films comprising an oxidizing agent is believed to be that, first, the metal film surface is oxidized by the oxidizing agent to form an oxidation layer, and the metal film surface is polished by shaving the oxidation layer with the abrasive. In this polishing method, since the oxidation layer on the metal film surface embedded in the furrows of the insulating film is not significantly contacted by the polishing cloth and is not reached by the shaving effect of the abrasive, the oxidation layer of the metal film on the elevated sections is removed as CMP proceeds, thus flattening the substrate surface (see Non-patent literature 1 below, for example).
Polishing solutions used for high pressure polishing (for example, 20 kPa or greater) comprise polymers having a constant amount of hydrophobic functional groups introduced therein (Patent literatures 3 and 4, for example).
Recent years have seen a demand for patterned substrates micromachined to high wiring density, and methods for lowering the polishing load during polishing are being investigated.